EVALUATING THE MICRONUTRIENT FERTILITY OF NIGERIAʼS SEMIARID SAVANNA SOILS

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Abstract
Using greenhouse cropping and chemical procedures, I evaluated the status of available copper and manganese in 55 representative soils of the seasonally dry Nigerian savanna. Both metals were extracted with 0.1 M EDTA in 1 N NH4OAc pH 7.0, and in addition, Cu was extracted with 0.1 N HCl and Mn with 0.05 N HCl + 0.025 N H2SO4. Thirty of the soils were cropped to cotton (Gossypium hirsutum L.) in two experiments (one for Cu and the other for Mn). Each crop was harvested after 42 days, oven-dried, and analyzed for the appropriate metal.Relationships among extractable Cu and Mn, uptake of the micronutrients under greenhouse conditions, and selected soil variables were evaluated through simple and multiple correlation and regression analysis. Extractable Cu levels appeared to be strongly related to organic matter levels and to a lesser extent, to the clay fraction. Extractable Mn was strongly related to pH and to a lesser extent, to soil organic matter. Plant uptake of the two micronutrients was best described by multiple regressions that included the extractable metal, percentage of organic matter, and percentage of clay as independent variables.The extractable Mn levels increased from the slightly leached Inceptisols in the far north of the country to the heavily leached, more acid Ultisols and Oxisols in the south, and the extractable Cu levels increased in the opposite direction. Double-acid and EDTA-extractable Mn ranged from 12.8 to 53.9 ppm (mean of 31.6 ppm) and 1.40 to 47.1 ppm (mean of 24.0 ppm), respectively. Dilute HCl- and EDTA-extractable Cu ranged from 0.54 to 1.69 ppm (mean of 1.03 ppm) and 0.49 to 1.50 ppm (mean 0.87 ppm), respectively. The Nigerian savanna soils appear to be adequately supplied with available Cu and Mn at present, and deficiency problems are unlikely in the immediate future. Using greenhouse cropping and chemical procedures, I evaluated the status of available copper and manganese in 55 representative soils of the seasonally dry Nigerian savanna. Both metals were extracted with 0.1 M EDTA in 1 N NH4OAc pH 7.0, and in addition, Cu was extracted with 0.1 N HCl and Mn with 0.05 N HCl + 0.025 N H2SO4. Thirty of the soils were cropped to cotton (Gossypium hirsutum L.) in two experiments (one for Cu and the other for Mn). Each crop was harvested after 42 days, oven-dried, and analyzed for the appropriate metal. Relationships among extractable Cu and Mn, uptake of the micronutrients under greenhouse conditions, and selected soil variables were evaluated through simple and multiple correlation and regression analysis. Extractable Cu levels appeared to be strongly related to organic matter levels and to a lesser extent, to the clay fraction. Extractable Mn was strongly related to pH and to a lesser extent, to soil organic matter. Plant uptake of the two micronutrients was best described by multiple regressions that included the extractable metal, percentage of organic matter, and percentage of clay as independent variables. The extractable Mn levels increased from the slightly leached Inceptisols in the far north of the country to the heavily leached, more acid Ultisols and Oxisols in the south, and the extractable Cu levels increased in the opposite direction. Double-acid and EDTA-extractable Mn ranged from 12.8 to 53.9 ppm (mean of 31.6 ppm) and 1.40 to 47.1 ppm (mean of 24.0 ppm), respectively. Dilute HCl- and EDTA-extractable Cu ranged from 0.54 to 1.69 ppm (mean of 1.03 ppm) and 0.49 to 1.50 ppm (mean 0.87 ppm), respectively. The Nigerian savanna soils appear to be adequately supplied with available Cu and Mn at present, and deficiency problems are unlikely in the immediate future. © Williams & Wilkins 1983. All Rights Reserved.

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